1. Field of the Invention
This invention relates to screw adjustment mechanisms for ink fountain blades and the like, and more particularly to a screw adjustment mechanism wherein the amount of looseness (thread backlash) between two threadedly mated parts can be easily adjusted to a desired minimum.
2. Description of the Prior Art
Threaded shafts (screws) are much used to change the positional relationship between two or more parts. Normally one of such parts is longitudinally movable but held against rotation about a mating screw, and hence is displaced axially of the screw and moved with respect to the other part on turning of the screw. Unfortunately, the amount of looseness of fit (thread backlash) that occurs between mating threaded parts is unpredictable, with the result that the adjusted relationship between the two parts can not be made as precise as is desirable without resort to expensive components.
But even expensive components are not a complete answer to the problem. Wear and tear resulting from use of the screw adjustment mechanism eventually results in a looseness of fit which makes precise adjustment of the part impossible. The problem becomes acute when different metals are in contact, and particularly so when one of the metals is a soft one like aluminum of which ink fountain blades are frequently made.
Existing technology includes many ways of adjusting for thread backlash where the threaded components act as an "in and out" adjustment of a mechanism. All methods employed to date require an assembly procedure which either requires extreme accuracy of the mating parts, or a calibrating adjustment to be made after final assembly of the constituent parts. All existing methods of accomplishing the desired results are either too expensive or difficult to adjust to allow their use in a predictable manner when many such assemblies are required. With the increased use of computer control of adjusting mechanisms, the need for reliable, inexpensive means of achieving improved fit in threaded mechanisms is rapidly exceeding the practicality of the means of achieving it.
Particular prior art includes U.S. Pat. Nos. 4,000,695; 4,655,133; 1,275,348; 2,583,640; 4,534,290; 4,581,994; 3,559,573; 3,730,090; and 4,058,058. U.S. Pat. No. 4,000,695 (Perretta) shows an ink fountain blade assembly wherein a screw 16 is used to adjust the matingly-threaded ink fountain blade 13 with respect to the assembly frame. U.S. Pat. No. 4,655,133 (O'Dea et al) shows the use of a spring 34 about a screw 36 to compensate yieldably for backlash. Showing similar arrangements are U.S. Pat. No. 1,275,348 (Wood); U.S. Pat. No. 2,583,640 (Faeber); U.S. Pat. No. 4,534,290 (Schroder et al); and U.S. Pat. No. 4,581,994 (Wildman). U.S. Pat. No. 3,559,573 (Hantscho) shows a differentially threaded screw 26 matingly engaging two threaded parts 20 and 22, but no backlash adjustment mechanism. U.S. Pat. No. 3,730,090 (Lamberg) also shows a differential thread assembly, but no backlash adjustment mechanism. U.S. Pat. No. 4,058,058 (Hantscho) shows use of a set screw 56 to hold a screw 41 in place with respect to its mating member, and use of a set screw 52 extending into a recess 54 to limit longitudinal movement of a blade 37.